The first phase of our study on the role of-ionic channels in plant motor cells has been completed. This work demonstrated that the plasma membrane contains depolarization-activated potassium channels that remain open for minutes and that the magnitude of the potassium flux through these channels is adequate to account for the loss of potassium previously measured in vivo during cell shrinkage. The next phase of our study involves examination of other types of channels and determination of the effect of calcium on the several channels. Both inward-rectifying channels and pressure-sensitive channels have been observed. We have also loaded plant cells with calcium dye as a first step in determining the role of calcium.